In a conventional air-conditioning circuit, the cooling fluid passes, in this order, through a compressor, a condenser, an expander and an evaporator before returning to the compressor. In the evaporator, the cooling fluid passes from a liquid phase or liquid/vapor phase to a vapor phase, absorbing heat from the air flow which thus becomes cooled. A conventional circuit such as this usually has running through it a cooling fluid consisting of a fluorinated hydrocarbon such as the one known by the name R134A.
Air-conditioning circuits through which a cooling fluid of supercritical type, such as CO2 for example, runs are also known.
One of the disadvantages with the known evaporators lies in the fact that their ability to cool the air flow depends on the operation of the compressor. In other words, the air flow is no longer cooled as soon as the compressor is stopped.
Now, in most motor vehicles, the compressor is driven via the engine and is therefore placed out of operation as soon as the engine is stopped.
In the context of anti-pollution standards, it is anticipated that motor vehicles of the “stop-start” type will be produced, these being vehicles in which the internal combustion engine is stopped when the vehicle is in neutral, then the engine is re-started when necessary, using an alternator/starter. The result of this would be that when a vehicle of this type was in neutral, with the internal combustion engine stopped, the air-conditioning would also be stopped. The stopping of the internal combustion engine causes the stopping of the compressor, hence causing the passenger or passengers of the vehicle to experience discomfort.
In order to overcome this disadvantage it has already been proposed for air-conditioning circuits to be produced that comprise, aside from the evaporator, auxiliary means for producing cold and which consist, for example, in providing a reserve of ice to cool the flow of air when the evaporator is not in operation. These known solutions are bulky and complicated to produce and prove to be somewhat incompatible with modern vehicles in which the space dedicated to the various equipment items, particularly in the engine compartment, is becoming increasingly cramped.
A similar problem may arise when the heat exchanger is produced in the form of a heating radiator through which a heating fluid runs, because this fluid is set in motion by a pump, also known as the “water pump”, which is conventionally driven by the vehicle's internal combustion engine. Thus, when the engine is stopped, this stops the pump and therefore stops the circulation of the fluid, hence giving rise to an experience of discomfort, especially when the exterior temperature is very low.